A thermoplastic resin is capable of being injection molded, and is employed in a variety of fields. In order that the resin may cope with requirement characteristics varying depending on the purpose of use, it is a prevailing practice that a plurality of resins are used in combination.
It is one example of the foregoing that a rubber based resin is added to a thermoplastic resin to enhance the impact resistance thereof, and an attempt is made to use a thermoplastic elastomer composed of a block copolymer as a rubber based resin.
There is available as the thermoplastic elastomer as mentioned above, for instance, a thermoplastic elastomer composed of an isobutylenic block copolymer as disclosed in Japanese Patent Application Laid-Open Nos. 301955/1996 (Hei-8) and 246733/1999 (Hei-11). However, the resin composition in which the above-mentioned thermoplastic elastomer was used has not been always satisfactory in aspects of hardness, loss properties, gas permeation resistance, injection moldability and the like.
In addition, there are proposed an elastic member for an ink jet printer, an insulator for a recording medium drive, a gasket for an HDD and an impact absorbing material for an HDD that are each constituted of a resin composition wherein a thermoplastic elastomer is used. The above-proposed items, however, each involve a problem as described hereunder.
In the first place, the elastic member for an ink jet printer will be described. An ink jet printer has heretofore been equipped with an ink chamber which is filled in with ink, and an ink tank having an ink supply portion which supplies a recording head portion with ink. Examples of the type of the ink tank include a constitution such that ink is supplied to a recording head which is stationary attached to a carriage via a tube which is arranged in a unit so that the ink tank is freely attachable to and detachable from the unit, a constitution such that the ink tank is integrated with a recording head so that the ink tank is freely attachable to and detachable from a carriage and the like constitution.
The configuration of supplying the recording head with ink is such that water head difference is set on the recording head in the former, whereas in the latter, a negative pressure source is provided on the ink tank side.
There have been proposed in recent years, more ink tanks in the form of the latter from the aspects of miniaturization of a unit and ease of maintenance work.
Any of these ink tanks for the ink jet printers is required to be capable of satisfactorily supplying the recording head with ink which counterbalances the amount of the ink discharged from the recording head at the time of recording and at the same time, to be free from ink leakage through a discharge port at the time of non-recording.
An example of the ink tank meeting with the above-mentioned requirement is an ink tank which is integrated with a recording head in which a cartridge is freely attachable to and detachable from a carriage, and which is filled inside with an absorbing body (foam). By filling an absorbing body in an ink tank in such a manner, it is made possible to preserve ink inside the ink tank by the capillary force of the absorbing body and thus maintain stable meniscus of ink at the ink discharge portion of the recording head. It is necessary in this case that the absorbing body be filled in almost whole of the ink tank. Thus by allowing the absorbing body to hold an amount of ink some what smaller than a maximum amount thereof that can be held by the absorbing body, internal negative pressure is generated by taking advantage of the capillary force. Accordingly, even in the case where there exists mechanical input such as vibration or thermal input such as temperature variation in the recording head or the ink tank, it is made possible to minimize ink leakage through a discharge port of the recording head or a communicating portion of the ink tank to atmosphere and thereby to carry out stable ink preservation.
Nevertheless the system in which the ink tank inside is almost wholly filled with the absorbing body involves a problem that the internal negative pressure is increased, accompanying the consumption of the ink, thereby increasing the amount of ink remaining in the ink tank without being supplied to the recording head, whereby the application efficiency is deteriorated.
In order to solve the above-described problem, there is proposed an ink cartridge which is used for an ink jet recording head and which is constituted, for instance, such that the ink tank inside is separated into an ink reservoir and a hollow portion by the use of a wall equipped with a communication hole on a lower portion, an umbrella check valve is movably installed on the communication hole, the check valve is opened at the time of point when the ink pressure in the recording head is lowered so that the ink in the ink reservoir is discharged in the hollow portion and supplied to the recording head {Japanese Patent Application Laid-Open No. 231759/1987 (Sho-62)}.
Since there is no need to house an absorbing body in a cartridge according to the above-mentioned constitution, substantial amount of the ink housed in the ink tank can be increased. However, there is in general a serious problem with an umbrella check valve in that its offset is too large to accurately regulate the ink feed rate to the recording head, thereby causing variation in the ink feed rate and also deterioration of printing quality.
On the other hand, since the ink reservoir and the recording head are completely interrupted in a state of the umbrella check valve being closed, in the case where the ink in the hollow portion is volumetrically expanded by 2 to 5% approximately due to variation in environmental temperature, there is caused a problem that an increase in the pressure in the hollow portion breaks a seal between the recording head and a connection port, thus causing ink leakage; and in a state of the ink tank being integrated with the recording head, there is caused a problem that the ink tank pressure acting thereon as such makes it impossible to maintain the negative pressure therebetween, thus causing ink leakage through the recording head.
Moreover, the umbrella check valve involves such a problem that pressure difference of several tens of water gauge pressure to be kept for stable ink supply to the recording head, which is too low to close the valve, brings about a fear that it is opened in response to the ink swinging action due to carriage movement and also deterioration in printing stability.
In order to solve the problem with the ink tank equipped with the aforesaid umbrella check valve, an attempt is made, for instance, to employ an ink tank valve which is located at the position where the ink chamber and the ink supply portion are separated from each other, is moved by the pressure difference therebetween, and supplies the ink filled in the ink chamber to the recording head {Japanese Patent Application Laid-Open No. 174860/1996 (Hei-8)}.
By equipping the ink tank with the ink tank valve, it is possible to surely supply the recording head with ink, while certainly responding to slight pressure difference between the ink tank and the recording head without being influenced by the ink swinging action due to carriage movement so as to maintain negative pressure well suited for printing and at the same time, it is enabled to prevent ink from leaking through an ink supply port due to temperature variation and/or through the recording head.
There are usually used in the ink tank valve, an elastic material exemplified by an elastic material adhesively bonded to a plastic substrate and the like, in which thermosetting rubber has heretofore been generally used as the elastic material. However the thermosetting rubber involves a problem of difficulty in injection molding by two-color molding with plastics, of a high production cost for the aforesaid valve and besides, of difficulty in molding and vulcanizing a member of a desirable shape by using a material having lowered hardness.
On the other hand, ink leakage from an ink tank for replacement has hitherto been prevented by attaching a foamed elastic member such as polyurethane foam thereto at an ink supply port, but a long-term use thereof makes it impossible to hold ink as the case maybe, whereby development of an elastic member excellent in durability has eagerly been desired.
In regard to the ink jet printer, in the case of a printer being unactuated, the recording head is made to stand by at the end of the main body of the ink jet printer. In order to prevent ink from leaking through the recording head in the case of this standing by, the recording head is housed on a sealing member placed along a recess provided on the main body of the ink jet printer.
Thermosetting rubber, which is usually used as the sealing member, involves the problem same as the foregoing.
As can be seen in Japanese Patent Application Laid-Open No. 978/2000 (Hei-12), there is filed a patent application concerning an elastic member which is used for an ink jet printer and in which a styrenic elastomer is used. Examples of the styrenic elastomers described in the patent gazette include SEPS, SEBS, SBS and SIS in which soft segment is polyethylene propylene, polyethylene butylene, polybutadiene or polyisoprene. As is well known as the information on rubber materials for general purpose use, these polymers are not necessarily excellent in gas permeation or moisture permeation. Thus the polymers, when being required of lower gas permeation performance or lower moisture permeation performance, sometimes results in failure to manifest satisfactory performances.
Next, the insulator for a recording medium drive will be described.
A drive for a recording medium wherein information is written in such as a CD, CD-ROM and optical disc is equipped inside with a recording medium driving portion which records and/or reproduces the recording medium, and on which are mounted an electric motor for driving a recording medium, a pickup means for recording and/or reproducing the recording medium and the like. The motor and/or pickup means are not resistant to vibration from outside and inside in an aspect of mechanism, and hence are equipped with an insulator composed of thermoplastic rubber or the like for the purpose of insulating the vibration.
As a construction material for the above-mentioned insulator for a recording medium drive, there have hitherto been used general purpose rubber which is exemplified by silicone rubber and butyl rubber, and which has a hardness of about 20 to 50 degrees in terms of JIS A hardness; a gel; an oil damper and the like.
The above-cited rubber material, which has a loss factor not sufficiently high, has frequently brought about a cause for malfunction owing to high vibration transmission rate at around the resonance frequency and insufficient vibration insulation upon writing in on a recording medium.
For these reasons, in the case of using a rubber material as a vibration insulation material, the vibration insulation properties which could never been attained in a low frequently region have been achieved by devising the shape of the vibration insulation material, for instance, by molding the material into an intricate shape through thin wall molding or the like.
Nevertheless, the thin wall causes deterioration of strength, liability to damage upon molding and thus difficulty in enhancing productivity. Further in the case of vulcanized rubber, problems are caused in that there is a concern that sulfur as a vulcanizing agent remains and influences electronic part items, and in that silicone rubber brings about possibility of contact trouble due to low molecular weight silicone.
For the purpose of achieving vibration insulation in a low frequently region, the use of a more soft material such as a gel is taken into consideration. However there is a concern that a low hardness material is liable to deformation due to compression, is deteriorated in vibration insulation properties with the lapse of time, and allows low molecular weight components in the material to bleed out, thereby exerting adverse influence on a disc requiring vibration insulation. Next, the gasket for an HDD will be described.
In recent years, electronic equipment such as a computer has come to have intricate circuit constitution, accompanying the progress towards a high performance and compactification, and is prone to be readily damaged even by a slight amount of dust. Accordingly, dust prevention is increasingly required in practical application, thus making it a usual practice to put a gasket on the junction surface between a box type main body incorporating the electronic equipment and a cover thereof, tighten the body and cover, and integrate the same by hermetical sealing. Further in order to simplify the handling upon use, there is frequently used a cover integrated with a gasket in which a cover and a gasket are integrated with each other.
However, owing to high densification of electronic part items, a gasket and sealing member are increasingly required that are more resistant to the permeation of dust and chemicals than conventional products and at the same time, are free form the generation of harmful outgas, namely free from chemical contamination.
Next, the impact absorbing material for an HDD will be described.
An actuator for a hard disc drive (HDD) is a device which locates the position of a magnetic head installed at the tip of the actuator which constitutes a part of a positioning mechanism for a high velocity head, and besides, records and reproduces magnetic signals on the magnetic disc by means of the above-mentioned magnetic head. The positioning of the magnetic head is put into practice by controlling the Lorentz force which is generated by a coil that is supported with a voice coil motor and an actuator through the control of electric current to be passed through the aforesaid coil.
The actuator is equipped in the vicinity thereof with a stopper mechanism termed crush stop which is intended to prevent a magnetic head and/or a head gimbals assembly from colliding with another member, falling out or being damaged in the event that a head positioning mechanism becomes uncontrollable and runaway by reason of malfunctioning or the like.
There has heretofore been prevalently employed as the above-mentioned impact absorbing material for an HDD, an elastic body composed of a thermoplastic elastomer of any of polyurethane base and polyvinyl chloride base. However, the impact absorbing material which is used for an HDD and made of the aforesaid elastic body has involved such problems as a large amount of harmful gas generation and insufficiency for use as a crush stop.